Communication system



1 com-z- ET AL 2,207,720 COMMUNICATION SYSTEM Filed July 19. 1958 l 7sheets-sheet 1 July 16, 1940.'

July 16, 19405 l. COLE Er A1. 2,207,720

' COMMUNICATION SYSTEM Filed July 19, `19758 '7 Sheets-Sheet 2 PMENTMOTOR. Il

PERFOPATOR E. COLE MEL/1055 /NVENTOPS 5A July 16, 1940. l. E. COLE ErAl.

COMMUNICATION SYSTEM Filed July 19, 1958 4ff sheets-sheet s ATTORNEYJuly 16, 194(3- .l l. E. COLE ET A1. 2,207,720

COMMUNICATION SYSTEM Filed July 19, 1938 7 'sneets sneet 4 VMIHI'HIIIIl-Ir I K WU int-.COLE

July 16, 1940. n. E. COLE ET AL.

COMMUNICATION SYSTEM Filed July 19, 41958 7 Sheets-Sheet 5 A5.com/NVENTORS Alim-H055 ATTORNEY July 16, 1940- 1. E. COLE ET' A1. 2,207,720

COMMUNICATION SYSTEM Filed July 19, 193s 7 sheets-sheet e July 16, 1940l. E. COLE ET AL COMMUNI CATION SY STEM Filed July 19. 1938 7Sheets-Sheet '7 ms Q5 E. COLE N VEN TOPS A. MEL/1055 ATTORNEY V PatentedJuly 16, 1940 UNITED STATES PATENT OFFICE .COMUNICATION SYSTEMApplication July 19, 1938, Serial No. 219,964

10 Claims.

'I'his invention relates to communication systems and particularly tocombined telephone and telegraph systems in which the telegraph signalsare interpolated in a telephone conversation.

Where long and highly expensive communication channels are employed, itbecomes economically desirable to use these facilities up to f'ullcapacity. Heretofore, systems for interpolating telegraph signals intelephone conversations have lo been devised which, under voice-operateddevice control, took advantage of every lull and pause in theconversation even down to fractional parts of a second for carrying on,telegraph transmission so that the channel was used practically one lhundred per cent of the time. For example,`

Patent 1,754,240 to Nyquist et al. granted April 15, 1930, and Patent1,895,461 to R. A. Helsing granted January 31, 1931, both show systemsin which telegraph transmission is carried on not n only in onedirection While speech is being transmitted in the other direction butalso in the other direction during the pauses in the speech.

It isan object of the present invention to improve systems of thisnature by providing special g5 means for insuring the correcttransmission of the telegraph signals without any interference with thetelephone conversations.

Accordingly, a feature of the invention is means to hold up andretransmit any telegraph 30 signal that has been partially transmittedat the time the voice-operated controls take over the circuit. VSincethe circuit used in this way is primarily designed for telephoneconversations,

the telegraph transmission must be immediately 35 cut off whenever asubscriber starts to talk and since these periods occur at randomprovision must be made to retransmit any telegraph code 'combinationwhich has been only partially transmitted.

In one embodiment of the. invention, the telegraph apparatus used at thereceiving end comprises a printer which responds to the telegraphtransmission and mechanically locks up devices selected by the codeimpulses and thus if a code 45 is cut oit at the transmitting end beforeit has been fully transmitted, the apparatus will be partially operated,but since under these conditionsv Another feature of the invention is ameans for permitting a code combination which has been almost completelytransmitted and hence almost completely received to reach completionwith a slight impairment of the speech. Actually this impairment ofspeech is only theoretical for it cannot be detected by the ear since itis only necessary to clip off the voice currents for a period of amaximum of a few milliseconds on rare occasions which occur when anumber of adverse conditions arise simultaneously. In practice and sincethis is a purely random occurrence, the clipping is rare andthe clippingfor the maximum period is still more rare, so that detection by alistener is practically impossible.

The system is operated by control currents accompanying speech.' Whenspeech starts the amplier detector means responds and starts the flow ofsuch control currents. For a certain y distance thek control vcurrentsand the speech are carried in diierent paths and delay circuits areintroduced in the speech path so that the control currents may betransmitted ahead in point of time in order to prepare the circuitsahead for the proper transmission of speech. vThere is in addition acertain delayA in the response of the amplifier detector means due to,and known as, syllabic variation and the measure of the delay in thespeech path is made of an order equal to or slightly greater than themaximum delay due to syllabic variation plusl the time required for theswitching operations carried out upon the arrival of the controlcurrents.

When a code has been transmitted up to a certain predetermined point,the starting of the iiow of control currents in response to the startingof speech anywhere between the predetermined point and the end of thetransmission of the code is delayed for a very short period. Under mostcircumstances, this delay will not be enough to hold up switchingoperations to the pointof clipping the speech. It is only when thespeech starts at the beginning of the predetermined point of codetransmission and when a maximum syllable variation delay has Vbeenencountered that any clipping of speech might take place. This is anextraordinary combination of circumstances and the probability that itwill occur is extremely remote. Practical working of the circuits hasled to the observation that it is undetectable by the listener.

This delay in the application of control current is controlled by thetransmitting yapparatus since the decision as to whether the receivingapparatus shall printor shall store must be kept at one point. Given avvariation in the time of transmission, and the -possibility of slighterror in synchronism, the telegraph circuits at the receiving end mustbe held intact for a period long enough to insure the correct receptionof the last pulse of a code under any combination of adversecircumstances. This will insure against any one of three errors whichmight otherwise occur, such as the omission of a character, the printingof a wrong character or the duplication oi' a character. Hence, theintroduction of a slight theoretical impairment of speech is entirelyjustied and the means for controlling this forms one of the novelfeatures of the invention.

As in other well-known voice-operated device anti-singingcircuitscharacterized Vodas, there is a speech hang-over means to keepthe established speech circuit intact without unnecessary switching. Inaddition, there is hereprovided another delay, known as a telegraphdelayed start which is introduced at the end of speech and which isprovided to prevent too many switching operations found by experience tobe unnecessary. Since it is intended that advantage be taken of allsmall lulls or pauses in the speech, the switching could be made to takeplace almost instantly at the end of speech, but since experience gainedby actual working shows that there is little to be gained by using thevery short lulls and pauses in the conversation, this telegraph delayedstart is introduced to minimize excessively frequent operation of theswitching means. This delay may be adjusted to any time interval greaterthan the speech hang-over and the decision of the telegraph apparatus tostart transmitting or not is controlled thereby. It has been found thata delay of one-tenth of a second is practicable, though the use of adelay oi. longer duration even up to a full second makes littlediiierence in the total amount of telegraph transmission.

The drawings comprise seven sheets. The rst of these, containing Fig. 1,shows the invention in schematic form and the rest when placed as inFig. 2 show the invention in diagrammatic form with certain well-knownelements, such as repeaters, ampliers, delay circuits, lters and hybridcoils indicated by labeled rectangles.

In general, as shown in Fig. l, a telephone conversation may be carriedon between subscribers connectedv to lines I and 2. The voice of thesubscriber on line I is directed through the hybrid coil 3 and thenceover the heavy line path 4 to the radio transmitting antenna 5 andthence to the radio receiving antenna 6 through the apparatusrepresented generally by box 1 which is identical with the apparatusshown in the rest of the ligure as connected to radioreceiving an tenna8, thence over a path therein corresponding to the heavy line path 9 toa hybrid coil and out to line 2 and to the subscriber thereon. The voiceof the subscriber on line 2 is transmitted from radio antenna I0 toreceiving antenna 8 over the heavy line path 9 through hybrid coil 3 toline I, and to the subscriber thereon. The invention is not limited tothe use of radio links as various other kinds of channels may be used.

The voice of the subscriber on line I traveling through hybrid coil 3,path 4, repeater II, transmitting suppressor I2 reaches path I4 where itencounters a delay and amplifier circuit I5 which delays the voicecurrents in reaching the antenna 5. From the path I4 a portion of thevoice currents flows over path I6 through an amplier detector I1 andthence to a voice-operated switching circuit I8. It will be noted thatcertain lines extend from this voice-operated switching circuit I8ending at various places in arrowheads. These indicate that thevoice-operated switching circuit has control over the other apparatus towhich the arrow-heads point. Thus,

.voice-operated switching circuit I8' has control over the transmittingsinging-suppressor I3, the control tone-enabler 20,--the control circuit25 for the two channels of the telegraph transmitting means, theswitching relays 26 for the two chancised by the voice-operatedswitching circuit I8 Y is to open this path at a proper time.

The voice-operated switching circuit i 8 under the inuence of voicecurrents from the subscriber on line I operates the transmittingsinging-suppressor I3 to open a clear path for the voice currentstraversing path I4 Switching circuit I8 at this time controls thecontrol circuit 25 to prevent telegraph transmission therefrom.Switching circuit I8 controls the switching relays 26 to give a clearpath for telegraph transmission from the channel A and B transmittersWithin box 1 into the receiving printers of channels A and B to the leftof box 26. At the same time switching circuit I8 opens the control fromtone-operatedfswitchingcircuit 2I to the control points indicatedthereafter so that such 29 and ythen transmitted from the antenna 5 tothe antenna 6. f

Within the apparatus designated generally by the box 1 the control toneand speech currents will be received by a radio receiver such as 30 andthence pass through the repeater 3I to the hybrid coil 32. At this pointthe speech currents, or as will later appear the telegraph currents,will traverse the path 33 since they encounter a bandelimination filter24 which will block oi the control tone. The speech currents passingtherefrom will next encounter a delay and amplifier circuit 22 and befed into the hybrid coil 23 and from thence through the receivingsinging-suppressor 34, the repeater 35, path `9, hybrid coil 3 to line2. The control tone which meets impedance by the band-elimination lter24 will leave the hybrid coil 32 and traverse the control tone lter 36which acts to block off the voice currents while passing the controltone. The control tone next encounters a control toneamplier detector 31and operates the tone-operated switching circuit 2I.

At the transmitting end, the voice-operated switching circuit I8 willhave the control path leading from tone-operated switching circuit 2Iopened but at the other end such control path will be closed and at thatpoint the receiving singing-suppressor 34 will be operated as well asthe transmitting suppressor I2 and the switching relays 26'. The delay22 is introduced so that the control tone will have ample time tooperate the switchingcircuit 2| before the voice reaches the path 9.

Thus while the voice of the subscriber is passing from line I to line 2,the telegraph apparatus for transmitting in the same direction isblocked oiI while the telegraph apparatus for transmitting inthe-opposite direction toward the receiving printers of channels A and Bshown in the lower left-hand corner of this gure will be placed inoperative condition.

If during the transmission of voice currents from line I to line 2, thesubscriber thereat should pause for more than a predetermined intervalof time, known as the voice hang-over, the voiceoperated switchingcircuit I8 will restore and then after another short interval, known asthe telegraph delayed start, telegraphic transmission will proceed fromchannels A and B indicated in the upper left-hand corner of this figureso that during such lull in the conversation telesraphic transmissionmay bey carried on simultaneously in both directions. During this periodif either the subscriberon line I or the subscriber on line 2 starts tospeak, the appropriate voice-operated switching circuit IB or itscompanion circuit within the box I will operate and stop the telegraphtransmission over the lines in the same direction in which the voice nowis transmitted.

IIhe invention in more detail is illustrated in Figs. 3 to 8, inclusive,when placed as indicated in Fig. 2.

It is believed that a short explanation of certain well-known pieces ofapparatus will help to a better understanding of the invention.

'I'he hybrid coil 38 when connected to line 39, and paths 40 and 4I andnetwork 42 is a circuit arrangement whereby voice currents entering thehybrid coil over path 39 will be transmitted over path 4B, and wherebyvoice currents enter- `ing the hybrid coil over path 4I will betransmitted to path 39. While transmission from line 39 emerges intoboth paths 40 and 4I, it is only effective in path 40 because therepeaters employed are unidirectional transmitting devices and suchtransmission can only pass through the repeater 43. Again, while waveenergy from path 4I enters equally into line 39 and network 42, itperforms no useful purpose in the network other than to insure goodtransmission into line 39 on account of the balancing properties ofnetwork 42. The transmitting repeater 43 is a well-known device forrepeating and amplifying voice currents in one direction, as indicatedby arrow.

'I'he next piece of apparatus, known as a transmitting suppressor, isa'cembination of two transformers 44 and 45 having their secondary coilsdivided into two parts and connected in a crossed circuit. A pair ofleads is taken from the crossconnections and led to the contacts of arelay 46. Under normal conditions, as shown.' with the relay contactsclosed', the transmission will freely pass through the transformers 44and 45 but when the contacts of relay 46 are opened then transmission issuppressed. With an arrangement of this kind, opening and closing thecontacts of relay 46 introduces little change in the impedancecharacteristics of the circuit.

Another piece of apparatus, shown as a circle with the designation VIwithin, is the volume indicator 41.y This is generally inthe form of ameter and in most cases, is a millivoltmeter. The amplifier detector. isanother well-known piece of apparatus which will respond to voicecurrents Yto operate a relay 49. The box 50,

' marked Delay and amplifier," is an electrical or electroacousticnetwork which will delay the voice currents for a given period; in thepresent instance, about twenty-three milliseconds. Since the delayinvolves a certain transmission loss, this circuit is combined with anamplifier to compensate for such loss so that the box 50 is actually ano-loss delay circuit. Next in line is a piece of apparatus known as atransmitting singing-suppressor. This is similar to the transmittingsuppressor heretofore described with the exception that the twotransformers 5I and 52 have their secondaries connected directlytogether. In this case, for transmission to freely pass through thisnetwork the connection between .the leads taken from the secondariesmust be open. In the position shown, with the contacts of relay 53closed, this transmitting singing-suppressor will prevent transmission.

Shown directly above this transmitting singing-suppressor is a signalconverter comprising two transformers 54 and 55 connected together inexactly the same arrangement as the transmitting suppressor heretoforedescribed. In this case, two sources of tone 56 and 51 supply current tothe transformer 54. When the leads from the secondaries of transformers54 and 55 are opened, then the tone from sources 56 and 51 is nottransmitted to the hybrid coil 58 but when these leads are closed, thenthe tone freely passes into this hybrid coil. It will later appear thatthe leads running from the secondaries of these transformers arecontrolled by a pulse relay so that when the relay contacts are closedmarking pulses comprising tones from these sources 56 and 51 will enterthe hybrid coil 58 and when the contacts are opened the absence of tonewill constitute a spacing pulse.

There are also shown on Fig. 4. certain rectangles designated asfilters, for instance, control tone filters 59 and 60. These, as well asother filters shown on the drawings, are of well-known type.

In Fig. 3 certain other pieces of apparatus are shown by conventionaldiagrams. For instance, a perforator 6I is indicated and a tape 62,perforated thereby, is shown leading to a box t3 which represents a.tape controlled transmitter. These are pieces of telegraph apparatus sowell known that further description is unnecessary. A rectangle B4 islabeled Motor and synchronous equipment. This represents the motivepower and the other apparatus controlled necessary for rotating -adistributor brush carrying shaft under exactly controlled conditions ofphase. Running from rectangle 64 there is indicated a shaft 65 carryinga number of sets of brushes moving over distributor faces which areindicated in a wellknown manner, In Fig. 5 there is a similardistributor, denoted here by rectangle 66, representing the motor andsynchronous equipment for this distributor. Rectangle B1 indicates,generally, a telegraph printer. The motor, ilve selecting magnets and aprinting magnet are indicated. y

It will be understood that the motor and synchronous equipment 64 forthe transmitter and 6.6 for the receiver are run in exact synchronism.

Similarly, the corresponding `pieces of apparatus in Figs. 6 and 8 arerunin exact synchronism and as will appear hereinafter, means areprovided to maintain synchronism between the distributors of Figs. 3 and5 and Figs. 6 and 8.

In. operation, if no voice currents are being transmitted over line 39and path 40 then the telegraph apparatus shown in Fig. 3 will be fullyenabled. Let us assume for the time being that relays 49, 68, 69, and 53are in the position shown. If tone from sources 56 and 51 is gettinginto the hybrid coil 58 it cannot feed back through the transmittingsinging-suppressor since relay 53 has the secondaries of transformers 5|and 52 short-circuited and such tone will yonly go out through hybridcoil 1D and radio transmitter 1| and antenna 12. Two frequencies areused to make telegraph tone and are widely separated and adjusted tovolumes such thatkeither or both frequencies received will. work thereceiving printing equipment. This insures against the adverse effectsof selective fading in the radio circuit.

The tape transmitter 63 has ve pins, such as 13, which will engageperforations in the tape 62. When this occurs, the contact 14 is movedfrom its lower contact 15 to its upper contact 16. The upper contact 16represents a marking condition and the lower contact 15 represents aspacing condition. When, in the course of operation of the distributor,the shaft 65 brings a brush into position to make the contact betweensegment 11 and ring 18, either spacing current from contact 15 ormarking current from contact 16 will be extended to the telegraphtransmitting line relay 19. If marking current is transmitted, then thepolar relay 19 will be left in the position shown, whereby thesecondaries of transformers 54 and 55 are closed and tone from sources56 and 51 is transmitted into,the hybrid coi'l 58 and thereafter outover antenna 12. If spacing current is transmitted to the relay 19,.thenthe armature will move to the left and the signal converter comprisingcrossed coil transformers 54 and 55 will prevent any tone beingtransmitted into the hybrid coil 58, thus establishing a spacing signalcondition.

Let us assume that the shaft 65 is just coming to a. position where itwill make a connection from segment 80 to ring 8| and where the brushworking on ring 18 will successively pass over the teries.

segments 82, 83, 84, 85 and 11 comprising the five code segments fromthe channel A transmitter.

Under the assumption that the voice circuit is not being used at thistime, the relays 88, 81, 88 and 89 will be in positions shown. As justpreviously, a connection has been made between ring 90 and segment 9|,thus connecting ground to the lower Winding of relay 92. have moved itscontact to the position shown so that battery is connected to one sideof the stepping magnet 93 in the channel A tape transmitter. 'I'hismagnet is not energized at this time. Since relay 81 is in the positionshown, the connection between common ring 8| and segment v isineffective and therefore relay 92 is left in the position shown. Now asthe brush successively passes over segments 82, 83, 84, and 11, themarking or spacing signal current, as the case may be, is transmittedthrough the back contact and armature of relay 94 to the contact andarmature of relay 86, winding of relay 19 to the common point of themarking and spacing bat- -As the brushes connected to shaft 65 passfurther along and are now in the position of transferring the recordfrom tape transmitter 95, a connection will be made from ring 96 tosegment 91 and thence to the other side of stepping magnet 93 so thatwhile the record from tape transmitter 95 is being transmitted the shaft98 of tape transmitter 63 will be rotated and the tape advanced to thenext set of code perforations.

Relay 92 will thenv In adsimllar manner, yduring the movement of theshaft 66 a connection will be made to segment 99 while the record fromtape transmitter 63 is being transmitted and shaft |00 will be rotatedthrough the energization of magnet |0I.y In this manner the record ofthe two transmitters will be `alternately transmitted by the relay 19.

Suppose now that voice currents are transmitted over paths 39 and 40.Amplifier detector 48 will pick up these voice currents and cause theenergization of transmitting master relay 49. This relay will cause theenergization of transmitting voice hang-over relay 88 and transmittingecho hang-over relay 69. Under normal conditions, a ground is extendedfrom the armature of relay 49 through its left contact to the leftcontact of relay 88 where it is connected to the armature and thisdirect ground connection on conductor |02, through the agency ofresistance |83, keeps the normal battery potential from affecting relays53 and |04. With this ground removed, transmitting singing-suppressorrelay 53 and transmitting telegraph enablerV relay |04 become energized.Relay 53 puts the transmitting singing-suppressor into condition so thatvoice currents will freely Apass from path 40 to thevhybrid coil 58.4Transmitting telegraph enabler relay |04 connects battery through itsarmature and front contact to the windings of relays 81 and 86 in seriesto ground, causing these relays to become energized. Relay 86 connects asteady spacing current to -relay 19 so that the signal convertercomprising cross-coil transformers 54 and 55 is put in condititon toblock out the tones from tone sources 56 and 51 so that such tones willnot, be mixed with the speech ,in hybrid coil 58. Relay 81 will bring upits armature to put ground on the ring 8|.

Now if the shaft 65 is in position where the brush is passing over anyone of segments 82 to 85, inclusive, then ground on ring8| will energizethe upper winding of relay 92, driving this relay to its spacing contactwhere auxiliary relay 94 will become energized. Relay 92, by moving itsarmature, removes the possibility of stepping magnet 93becomingenergized and relay 94 opens the connection between ring 18 and the backcontact of relay 86. As long as transmittingtelegraph enabler relay |04remains operated, relays 86 and 81 will remain operated and both thetransmission relays 92 and |05 will be kept on their spacing contactsand the tapes for both of the tape transmitters will remain. stationary.Actually each time a connection is made between ring and segment 9| orsegment |06, relay 92 or |05 will be driven to its marking contact butimmediately thereafter as a, connection is made betweenring 8| andsegment 80 and so forth, the relay 94 or |05 will be driven back againto its spacing contact. As soon as the telegraph transmitting enablerrelay |04 becomes deenergized and thereafter when a connection is made`to either segment 9| or |06, the corresponding relay 92 or l 05 will bedriven to its marking contact and since ground will now be removed fromring 8|, transmission from the tape transmitter will be resumed.

If relay |04 becomes operated while a connection is being made betweensegment 11 and ring 18 or, in other words, at the same time as contactis being made between segment |01 and ring |08, then a connection willbe established from battery, ring |08 and segment |01, -windings ofrelays 89 and 88 in series, back contactv effect of the operation ofrelay |04 isnullied' until the brush on shaft 65 leaves segment |01.During this very brief period the control tonedisabler relay 89 opensthe connection between crossed coil transformers |09 and ||0, formingthe control tone-disabler, so that even though the voice may now takecharge of transmitting master relayl 49 and thereby cause theenergization of control tone-enabler relay the transmission of controltone from the sources ||2 and I I3 is held up. The delay thus introducedin the transmission of control tone is enough to allow,

the completion of the code while the brush is passing over segment 11.This enables the receiver at the other end of the channel to properlyrecord the code. Even when this relay in the transmission of controltone through the operation of control tone-disabler relay 89 takes placejust as a connection is being established between segment |01 and ring|08, the delay introduced is not of greater magnitude than the delayintroduced in the speech path by the delay ampliiier 50 and otherapparatus which the* speech encounters further on. It should be notedthat if the voice takes charge of transmitting master relay 49 beforeconnection is made between ring |08 and segment |01 by even theslightest interval that the resulting energization of relay 81 willprevent the energization of control tone delay relay 89.

As the transmission from antenna 12 is received over antenna ||4 andthence by the radio receiver ||5, the control tone when it is nally putonto hybrid coil 10 by the'release of relay 89 will pass through thecontrol tone filters I6 and ||1 and thence through the controltone-ampliiler detector ||8, causing the operation of relays ||9, |20,|2| and |22. Relay |20, known as the receiving singing-suppressor relay,takes a short circuit off the secondaries of transformers |28 and |24,thus opening the path for voice currents to go through the receivingrepeater |25 and hybrid coil |26 to the line |21. Since the voice cominginto radio receiver |5 encounters another delay |28 of approximatelytwenty-three milliseconds, itvwill be seen that the delay to controltone introduced by the operation of control tonedisabler relay 89 willnot actually affect the speech. Since the control tone operating relay|2| allows the printer slow-operate relay |29 to release and since therelease of this relay starts in motion a chain of other operations tostop the printing of characters by the twoprinters |30 and |3|, it isnecessary to introduce this short delaywhich equals that incurred indelay |28 in order to insure the printers |30 and |3| completing theiroperation.

It will be noted that the sources of tone 2 and ||3 are marked,respectively, 150 cycles and 3000 cycles, and that the control tonelters 59 and 60 are also marked, respectively, 150 cycles and 3000cycles. These two tones are used as extra band frequencies in accordancewith wellknown practice to render such control tone distinctive andseparable fromthe voice band frequencies. 'Ihe control tones are of suchvolume that either or both of the frequencies can operate the receivingcircuit in order to reduce the ||1, which again are marked,respectively, 150

cycles and 3000 cycles. After this, the outputs of these filters arecombined and enter the control tone-ampliiier detector ||8 from whichthe relays ||9 to |22 are operated. The armature of control tone masterrelay |9 is subject 4to vibration at the lower frequency and hence ahangover circuit consisting of -two resistances |31 and |38 and acondenser |39 is provided to render the other relays |20 and |2| incircuit therewith not subject to such vibration. The last relay in line,|22, known as the receiving echo hang-over relay, must be given anotherslight delay in returning to normal and hence another hang-over circuitcomprising resistances |40 and |4| and condenser |42 is provided andoperated by the receiving printer master relay |2|. The receiving echohang-over relay |22 by opening the connection between the cross-coils ofthe two transformers |45 and |46, is provided to y block any echo thatmight otherwise be transpressor relay |20. Thereafter the voice passesthrough the receiving repeater |25 into the hybrid coil |26 and to thesubscriber on line |21.

Let it be assumed that telegraph tone pulses are being received byantenna H4.. These ,tones will pass through hybrid coil |48 intoattenuator |49 and thence through two filters |50 and' |5| which, likeother lters, are constructed and arn ranged to pass the frequenciestransmitted from the sources 56 and 51. The filtered tones then enterhybrid coil |52 and through the amplifier detector |53 operate thereceiving telegraph master relay |54. Such tones, representing a markingpulse, willl bring relay |54 to its front contact and thereforeestablish a circuit from the armature of printer hang-over relay |50,its back contact, the armature and front contact of relay |54 and theupper windings of receiving telegraph line relay |55, auxiliaryreceiving relay |69 and corrector relay |56 to battery. These threerelays will move their armatures to their marking contacts, as shown.Receiving telegraph master relay |54 responds to the code impulses bymovingv its armature into the position shown for marking impulses andreleasing it to the other position for spacing impulses. three relays|55, |69 and |56 will follow and accordingly move their armatures eitherto their marking or spacing positions.

The vmotor and synchronous equipment |51 moves a shaft |58 in. exactsynchronism with the shaft 65. of the transmitting apparatus in Fig. 3.Hence, as the marking or spacing impulses applied to ring 18 are sentout and received by the relay |54, corresponding impulses will be placedon the ring |59 and as the brush which connects this ring to the row ofsmall segments above passes 'over these small segments it will, in eect,connect the selecting magnets |60, |6I, |62, |63 and |64 of channel Aprinter, respectively, to the five contacts of channel A transmitter,ending Awith contact 14. Hence selecting magnets |60 to |64, inclusive,will be operated in accordance with the perforated tape 62. As the shaft|58 moves The` on to the next set of segments associated with ring |59,the selecting magnets of printer |3| will, in effect, be connected tothe contact of the tape transmitter 95. While impulses are beingreceived by receiving telegraph master relay |54, printer slow-operaterelay |29 will be energized and hence printer hang-over relay |50 willbe deenergized and the receiving check relay |65 will be in the positionshown,that is, deenergized. Therefore, as the brush on shaft |58 whichconnects to ring |66 passes over those segments having to do withchannel A, the relay |61 whose upper winding is connected to segment |68will be unaffected. The operation ofauxiliary relay |69 during a markingimpulse closes a connection from ground through its armature and markingcontact to ring |10 and thence to segment |1| through the appropriatebrush on shaft |58 to the lower winding of relay |81 to positivebattery. This drives relay |61 to its marking contact as shown, andsince this is a polar relay and will keep its armature where last placeduntil it is energized in the opposite direction, this relay will remainas shown until relay |65 is energized. Now as the shaft |58 moves alongand is controlling the set voi" selecting magnets of channel B printer3| a connection will be made between ring |12 and segment |13 which willcause the energization of printer magnet |14. Since if shaft |58 getsbeyond the five small segments connecting selecting magnets |60 to |64,inclusive, the relay |61 cannot be driven to its spacing contact againuntil the shaft gets back to near the position shown. 'I'he small delayto the control tone .introduced at the transmitter by the controltone-disabler relay 89 will insure the last of the selecting magnets|64being properly operated and thereafter the printer magnet |14. If thecontrol tone from sources |I2 and ||3 comes on before the shaft |58 hasreached the position for affecting selecting magnet |64, then relay |29will become deenergized and this will result in the energization ofchecking relay |65, whereupon battery is connected through ring |66 andsegment |68 to the upper Winding of relay |61 to drive this relay to itsspacing contact and thus prevent the energization of printer magnet |14.

Whenever a spacing impulse is received by receiving telegraph masterrelay |54 and hence the relay |56 is moved to its spacing contact,condenser |15 is charged. When the relay |56 is driven to its markingcontact, this charged condenser is connected through the armature andmarking contact of this relay to ring |16, whence it discharges eitherinto conductor |11 or |18 depending on the exact position of the brushtraveling over ring |16. Conductors |11 and |18 lead to the two windingsof auxiliary corrector relay |19 and, this relay being polarized andspring centered to stay in the position shown, will momentarily move itsarmature in either one direction or the other. Under the bestconditions, when the shaft |58 is in exact synchronism with the shaft65, the two windings of relay |19 will be equally energized and hencethe relays |88 and |8| are not energized, resulting in the stationaryresponse of indicator |82. Such an indicator is put lin at this pointmerely to indicate the method of correcting the speed of the motor andsynchronous equipment |51, since methods of actually doing this are wellknown in the art. If the shaft |58 begins to lag in time relation to theshaft 65, then the armature of relay |19 will tend to stay for a,greater proportion of the time on its left contact, thereby operatingthe slow-indipresent invention other than to illustrate a method ofkeeping the shafts of the transmitters and printers in synchronism. f

'Ihe apparatus lshown in Fig. 6 is a duplicatev of the apparatus shownin Fig. 3 and is used for transmitting telegraphic messages out overantenna |83 into antenna |84 and thereby operating the printer mechanismshown in Fig. 5. This, again, is a duplicate of the circuits andmechanism shown in Fig. 8.

As has been generally explained in connection with Fig. 1, both thetelephone and interpolated telegraphic transmission may be carried on inboth directions at the same time, that is, i-f voice currents aretraveling from the path 39 to the line |21, telegraphic messages may betransmitted simultaneously from the transmitters of Fig. 6 to thereceivers of Fig. 5. If there comes a pause in the voice currents thenthe messages Astored on the tape of the transmitters of Fig. 3

will be transmitted to the printers of Fig. 8. In practice, pauses ofthe nature of even a fraction of a second are used for this purpose andperfect transmission of telegraph code is insured by the provision ofmeans for stopping the transmission of a code message at any point inthe code and retransmitting this same code again when the telegraphicapparatus is enabled.` The addition of the means for holding up thecontrol tone for a very short time when the speech comes on durv ing thelast impulse of a series of code impulses so that the printer at theother end may operate, is of great importance in the prevention ofprinting errors. Practically, it has been found that due to delaysapplied to voice currents in these circuits, this delay to the controltone does not adversely affect speech.

What is claimed is:

1. In a communication system, a transmissionr channel, a permutationcode sender normally connected to one end of said channel, a receiverresponsive thereto normally connected -to the other end of said channel,voice-operated means for operatively disconnecting said sender and saidreceiver from said channel, and means in said sender for storing anycode partially transmitted upon disconnection and for retransmitting infull such partially transmitted code when transmission is resumed.

2. In a communication system, a transmission channel, a permutation codesender normally connected to one end of said channel, a receivedresponsive thereto normally connected to the other end of said channel,switching means for operatively disconnecting said sender and saidreceiver from said channel and for rendering said channel suitable forvoice transmission, amplifier-detector means responsive to voicecurrents for operating said switching means and meansy in said senderfor storing any code partially transmitted and for retransmitting infull such partially transmitted code when transmission is resumed. y

` 3. In a communication system, a transmission channel, a normallyoperating permutation code sender connected to one end of said channel,a normally operating receiver responsive thereto connected to the otherend of said channel, voice controlledswitching means for operativelydisconnecting said sender'and said receiver from said channel, meansoperative during the transmision of a code up to a given percentage ofits length upon the operation of said switching means for storing andpreparing for retransmission of such a partially transmitted code andmeans operative during the transmission of a code beyond said givenpercentage of its length for delaying the action of said switchingmeans.

4. In a communication system, a. transmission channel, a normallyoperating'permutation code sender connected to one end of said channel.a normally operating receiver resposive thereto connected to the otherend of said channel, switching means for operatively disconnecting saidsender from said channel, switching means responsive to a control tonefor operatively disconnecting said receiver from said channel, meansresponsive to voice currents for operating said first switching meansand for applying control tone to said rchannel for operating said secondswitching means, means responsive to the operation of said firstswitching means before the transmission of a given percentage of acomplete code for storing and preparing for the retransmission of saidpartially transmitted code and means for delaying. the application ofcontrol tone to said channel when the operation of said rst switchingmeans occurs after the transmission of said given percentage of acomplete code.

- s 5. In a communication system, a transmission channel, a permutationcode transmitter normally connected to one end of said channel, aprinter responsive thereto normally connected to the other end of saidchannel, voice-operated switching means for stopping the operation ofsaid transmitter and printer when operated prior to the transmission bysaid transmitter of a given percentage of a complete code and means fordelaying the operation of said switching means when operated subsequentto the transmission by said \\transmitter of said given percentage of acomplete code.

6. In a communication system, a transmission channel, a permutation codetape transmitter normally connected to one` end of said channel,sprinter responsive thereto normally connected to the other end of saidchannel, voice-operated switching means for operatively disconnecting.said transmitter and said printer from said channel and for halting thefunctioning thereof, means for storing and retransmitting a codetransmitted for less than a given percentage .of its total length andvoice delay means for insuring the printing oi' a character representedby a code and for advancing the tape in said transmitter when a code hasbeen transmitted for more than a given percentage of its total length. l1

7. In a communication system, a transmission channel, a. permutationcode sender at one end of said channel, a receiver responsive thereto atthe other end of said channeL-'synchronously running distributors forfeeding code impulses from said'sender into said channel and from saidchannel into said receiver, voice-operated switching means for stoppingthe flow of said code impulses and for preventing the functioning ofsaid sender and said receiver and means operative upon the release ofsaid voice-operated means for entirely retransmitting any code parytially transmitted before stoppage.

8. In a communication system, a transmissiony channel, a permutationcode sender at one end of said channel, a receiver responsive thereto atthe other end of said channel, synchronously running distributors' forfeeding code impulses from said sender into said channel and from `saidchannel into said receiver, voice-operated means for halting thefunctioning of said sender and said receiver up to a given point in therotation of said distributors and means for delaying the action of saidvoice-operated means beyond said given point inthe rotation of saiddistributors, said given point being fixed sufficiently near the end ofa code to insure the completion of the functioning of the said senderand said receiver Without noticeable penalty to speech.

9. In a communication system, a transmission channel, a permutation codesender, a receiver responsive thereto, synchronously running dis-ltributorsl for feeding code impulses from said sender into said channeland from said channel into said receiver, voice-operated devices forinterrupting the transmission of code impulses at random and means forresuming the transmission of code impulses only at the beginning of acode.

10. In a ommunication system, a transmission channel, a permutation codesender having a magnet for advancing to another code when one code hasbeen completely transmitted, a receiver responsive to said sender andhaving a recording magnet for recording acode completely transmitted bysaid sender and for preparing to receive another code, synchronouslyrunning distributors for feeding code impulses from said sender intosaid channel and from said channelinto said receiver, voice-operateddevices for cutting off transmission o1' code impulses at ran- 1

